Many many years ago...
Young, dumb, and full of ideas! We had a pile of RR tie pieces to cut up.
I created (I have a long history of creations) a table mounted chainsaw!
1/2 hp washing machine motor, 16" B&C. It ran slow enough that the gauge teeth were filed off. Ties are full of grit and would dull a regular saw in two cuts. This thing cut over a cord without being sharpened.
It was a dangerous experiment, but worked none the less.
If I wanted a chainsaw cut off saw I would think about using a horizontal 4 stroke briggs style engine. Should not be to much engineering to rig a sprocket and bar onto the thing. Add a oiler, make it swing in, or maybe just up and down with a counter weight. Hmmmm. make it a vertical shaft motor and use it on a saw mill. Hmmmm....
-pat